Solar cell teams plastic and
carbon

Today's solar cells are relatively expensive
because they are made from the computer chip material silicon, which requires
relatively expensive manufacturing processes including clean rooms.

It is possible to make solar cells from cheaper, easier-to-work-with
materials, including organic, or plastic-based materials. The trick is
finding inexpensive materials that are also efficient.

Researchers from the Georgia Institute of Technology have fabricated
an inexpensive, plastic-based solar cell that has the potential to be
fairly efficient.

Most organic photovoltaic cells are based on amorphous or nearly
amorphous organic materials. In contrast, the Georgia researchers are
using pentacene, a polycrystalline organic semiconductor. Polycrystalline
materials, unlike amorphous materials, consist of crystal grains that
have a lattice-like molecular structure. Pentacene is widely used in organic
transistor research.

The researchers' device consists of a glass plate, a layer of
indium oxide, a layer of pentacene, a layer of carbon buckyball molecules,
a layer of bathocuproine, and an aluminum electrode. The pentacene-carbon
portion forms a semiconductor junction that separates negative electrons
from positive holes to generate electricity. The researchers have measured
a power conversion efficiency as high as 3.4 percent for the material.
It will not be difficult to boost the efficiency to 5 percent, according
to the researchers. Existing organic solar cells are about 3.5 percent
efficient, while state-of-the-art crystal silicon solar cells are about
25 percent efficient.

The method could be used to power radiofrequency ID tags and sensor
networks. It could also eventually be used for solar cells that generate
residential power, according to the researchers.

The method could be used for powering sensors within two years
and for residential solar cells within five years, according to the researchers
and. The work appeared in the November 29, 2004 issue of Applied Physics
Letters.